This invention relates in general to wireless communications, and more specifically to a micro-slot antenna.
Prior-art antennas used in portable wireless devices have included loop, ceramic chip, and microstrip patch antennas. The loop antenna is inexpensive, but does not perform well in free-field conditions. The ceramic chip antenna is relatively expensive and has moderate performance both in free-field and on-body environments. The microstrip patch antenna is very expensive and does not perform as well on body as in free-field.
The loop and chip antennas are predominantly vertically polarized, and their performance degrades when incoming signals have a non-vertical polarization. The microstrip patch antenna has both vertical and horizontal polarization, but it is not favorable in terms of size, weight, cost, and bandwidth.
Thus, what is needed is an antenna that has a small size, light weight, low cost, wider bandwidth, and both vertical and horizontal polarization. The antenna preferably will have excellent gain in both free-field and on-body environments.
An aspect of the present invention is a micro-slot antenna for use at a predetermined wavelength. The antenna comprises a rectangular dielectric substrate having two long edges and two short edges; and a U-shaped conductive strip attached to a first surface of the substrate, the U-shaped conductive strip having two side members, each about one-eighth the predetermined wavelength in length, and an end member forming a substantially rectangular slot extending parallel to the long edges, the slot closed at a first end by the end member, and open at a second end. The antenna further comprises a microstrip feed line attached to a second surface of the substrate opposite and parallel to the first surface for coupling an RF signal between the antenna and an RF device, the microstrip feed line extending across and perpendicular to the slot proximate the second end of the slot, and further extending across a portion of the two side members; and a ground point electrically coupled to a first one of the two side members of the U-shaped conductive strip and positioned proximate the second end of the slot.
Another aspect of the present invention is a radio device comprising a radio element including at least one of a transmitter and a receiver, a user interface coupled to the radio element for interfacing with a user; and a micro-slot antenna coupled to the radio element for use at a predetermined wavelength. The antenna comprises a rectangular dielectric substrate having two long edges and two short edges; and a U-shaped conductive strip attached to a first surface of the substrate, the U-shaped conductive strip having two side members, each about one-eighth the predetermined wavelength in length, and an end member forming a substantially rectangular slot extending parallel to the long edges, the slot closed at a first end by the end member, and open at a second end. The antenna further comprises a microstrip feed line attached to a second surface of the substrate opposite and parallel to the first surface for coupling an RF signal between the antenna and the radio element, the microstrip feed line extending across and perpendicular to the slot proximate the second end of the slot, and further extending across a portion of the two side members; and a ground point electrically coupled to a first one of the two side members of the U-shaped conductive strip and positioned proximate the second end of the slot.